In 2013, Dr. Gerard Talavera was invited to partake in a biogeography workshop in Cayenne, the capital of French Guiana on the northeast coast of South America. He gladly accepted – the trip was a great career opportunity, but it also awarded him the chance to conduct some biological detective work and investigate a hypothesis he had been considering.
Talavera is a senior researcher and principal investigator at the Botanical Institute of Barcelona (IBB), where his research focuses on the behavior, ecology, phylogeography and genome evolution of migratory insects. He established the Insect Migration and Phylodiversity Lab and leads the Spanish National Research Council (CSIC) research group on Entomology and Insect–Plant Interactions.
Around the time of the workshop, Talavera had received anecdotal reports that Vanessa cardui (V. cardui), also known as the “painted lady” butterfly, had been spotted on the shores of French Guiana. This beautiful black, orange and white butterfly – now renowned for its trans-Saharan flights – is widespread around the world, but is not found in South America, typically.
If the painted lady was indeed present in French Guiana, had it traveled all the way across the Atlantic Ocean from Africa, a distance of at least 4200 km, likely without rest? If so, then how?
Talavera embarked on his journey to South America in search of butterflies and answers, both of which he successfully found.
The trip marked the beginning of a 10-year collaborative study involving researchers from the W. Szafer Institute of Botany, the University of Ottawa, the Institute of Evolutionary Biology (IBE, CSIC-UPF) and Harvard University. It culminates in a Nature Communicationspaper that provides empirical data on the transatlantic crossing of an individual insect for the first time.
Talavera and colleagues integrated data from population genomics, pollen metabarcoding, isotope-based geolocation and wind and energetic modeling techniques. Combining these approaches – some of which are next-generation – the researchers were able to reveal multiple details of the crossing event and overcome many of the limitations normally associated with tracking migrating insects.
The painted lady butterflies on the shores of French Guiana had indeed migrated from West Africa, they found, a journey that was energetically feasible only through assistance from favorable wind conditions.
In an interview with Technology Networks, Talavera discusses the particulars of the study, how it felt to conclude his detective work and how this unique methodology could be applied to study transoceanic dispersal in other insects.
Molly Coddington (MC): Can you expand on why you were inspired to complete this research project, and how you felt when you discovered painted lady butterflies on the coast of French Guiana?
Gerard Talavera (GT): I traveled to French Guiana with a hypothesis at hand. Based on scattered observations and personal communication with some colleagues in the region, I thought that the Atlantic coasts of South America were receiving occasional immigrants of V. cardui. But no one had given much importance to this before.
Part of my trip’s aim was to investigate if I could find any established populations or if I could find individuals on the beaches, where I’d expect them to be if they were migrants. After the biogeography workshop, I traveled around to collect butterflies.
After several days of monitoring lots of habitats, I couldn’t find any signs of the butterfly or breeding in their larval hostplants. I expected this, I suppose, as I was searching for the impossible. Then, on the very last day of my trip, while walking on a remote beach, I saw one butterfly “jumping”, as opposed to flying.
It took me a few seconds to react, but I recognized it and caught it with my net. I confirmed the identification visually – it was V. cardui – and two meters along the shore I caught a second one, and then a third. I saw about 10 in total, but as the sun was rising and the butterflies were warming up, they started to fly into the forested areas next to the beach, where I lost them.
I knew these butterflies were immigrants, and that this was an amazing finding. I had the samples, which was the most critical step to performing any further research. Without samples, this would have become yet another scattered record, without the possibility of producing data to investigate the butterfly’s movements.
At that time, I was starting a long-term research project to study the migratory movements, the ecology and the evolution of migration in V. cardui. This finding “gave me wings” to continue.
Since then, I have been working intensely to develop V. cardui as a model for insect migration research. My colleagues and I have contributed extensively to unraveling the natural history and migration of this species.
MC: The methods used in this study are quite unique. Can you tell us more about them?
GT: Tracking migratory movements in insects is extremely complex and no perfect solution exists. Insects are small and short-lived, and that excludes the possibility of setting up tracking devices as we do with birds, fish or mammals – at least for long-distance-migration studies. Furthermore, we can’t track movements from origin to destination, only backward from destination to origin.
Until now, researchers studying insect migration have relied on finding indirect evidence of long-distance movement based on observational data (e.g., massive sudden appearances of insect species, or species identification of individuals out of their range) or through technology that provides a “snapshot” of movement, such as radar technology that detects when large flocks of insects pass through a specific point at a certain altitude. Another commonly used indirect approach is to associate wind currents with observational or monitoring patterns.
This sort of evidence, however, does not inform us about connectivity, origin or destination. Also, commonly used techniques do not use actual specimens in any way to obtain empirical data, and most evidence obtained is based on modeling.
Our study combines, in a novel way, a set of methodologies that allows you to trace back the journey of the butterflies in an unprecedented way. These methods are as follows:
Pollen metabarcoding: We isolated pollen grains from the bodies of the butterflies and sequenced their DNA. We used DNA to identify the plants and then investigate their distribution. We found DNA from plants that only occur in tropical Africa.Isotope-based geolocation: Stable isotopes can be used to trace the natal origins of the butterflies. These isotopes have specific signatures over the geography. From the soil, these are transferred to the plants that are eaten by the caterpillars that later become adult butterflies. These butterflies keep the same isotopic signature from the site where they were born. As migratory butterflies move, these are likely to be captured in sites where isotope baselines are different and thus, we can trace back the most likely origins.Population genomics: We sequenced the genomes of V. cardui butterflies from three continents: America, Europe and Africa. We compared the genomes for population assignments of the South American individuals and found that they are more similar genetically to European/African populations than to the American population.
Wind and energetic modeling: We modeled wind trajectories for the date of capture, after and before, and showed that winds were favorable at different altitudes [for these butterflies] to have come straight from West Africa. We calculated the speed of these winds, together with fat consumption analyses for the butterflies and self-speed, and estimated the time and energy demands of the crossing, considering wind assistance.
Our study used evidence that, only when combined, can explain the different steps of a migratory journey.
MC: How did you feel when your data confirmed that the butterflies had crossed the Atlantic Ocean?
GT: I think I knew from the very beginning and was not totally surprised, as this had been my main hypothesis. It wasn’t until 2014–2016 that we proved the butterfly crossed the Sahara Desert from Europe every year, establishing the bulk of the population in the African Savannah.
After that, it was logical to think that in the massive movements south, some butterflies might get lost in the ocean. We know, for example, that the Canary Islands receive migrant inflows every fall season. I found this hypothesis more plausible than an inland corridor from Mexico, for example.
This species does not like rainforests and very wet environments, it’s not its habitat, so this has to be a barrier. Indeed, no established populations occur in Central America. Immigration from some Caribbean islands could be possible, but the species is rare there as well.
The first evidence I collected about the trans-Atlantic crossing occurred a few days after my trip, when I ran a preliminary analysis of wind patterns and saw a perfect correlation. So, to me, my hypothesis was clear. The main question was whether we would be able to prove it with empirical data!
After completing DNA analysis, which took me several years, we were able to confirm that the individuals belonged to the African/European population. Still, this did not prove that the individuals were the immigrants – they could be their offspring (although no breeding cases have been reported in French Guiana or anywhere else in South America).
At that point, I started collaborating with Dr. Tomasz Suchan and we developed the pollen metabarcoding protocol. It worked, and when we discovered that we detected the African plant it was a very exciting moment! Shortly after, I started collaborating with Clément Bataille, an expert on isotope ecology, and we ran hydrogen isotope analyses. These confirmed the butterflies were not locally raised, but the resolution on the potential origin was too broad. So, in a last effort, we analyzed a second isotope, strontium, which provided the best resolution to indicate a potential European origin.
MC: In your opinion, what are the key implications of this research?
GT: We show the remarkable dispersal and physiological capacity of some insects and flag a case that could help in raising the study of migratory insects in a more direct way. We also develop methodology to make that possible.
We show that long-distance dispersal across oceans is possible and that we may have underestimated these events. Long-distance dispersal has had to impact biogeographic patterns and the distribution of species over time.
Migration in insects is understudied. I often make the joke that there are more reviews about it than actual studies providing data. But these are extremely important for ecosystems: insects are the most diverse group of animals on earth (in species and biomass), and they move. These are generally in alarming decline, but they may move if they can, and global change is leaving that scenario open.
MC: What are your next research steps?
GT: We are studying migration in insects in a broad and interdisciplinary way. We have built a nice consortium of colleagues who are now working together across many topics. In our lab, we are studying the interface between environment and genomics, and how insects read environmental cues and respond with migration.
We are also tracing long-range migratory movements of several other species of insects (including butterflies, dragonflies and moths) and integrating new tools into our repertoire, such as remote sensing and satellite-based images. We are quite focused on trans-Saharan migrations, a phenomenon that has surprisingly only been shown for V. cardui so far.
Dr. Gerard Talavera was speaking to Molly Campbell, Senior Science Writer and News Team Lead at Technology Networks.
About the interviewee
Gerard Talavera is currently a CSIC Tenured Scientist at the IBB, where he has established the Insect Migration and Phylodiversity Lab and is leading the CSIC research group on Entomology and Insect-Plant interactions. His current research focuses on the study of behavior, ecology, phylogeography and genome evolution of migratory insects. To this purpose, he combines genomics, phylogenetics, and phylogeography with ecological modeling, isotope ecology and behavioral tests to jointly track insect seasonal movements and understand the evolutionary processes involved in the migration strategy and its ecological consequences. His contributions in this field have been particularly influential in positioning the migratory butterfly V. cardui as an emerging model system for ecology and genetics of insect migration.
Talavera started his research career in 2004 at the Institute of Molecular Biology (CSIC, Barcelona), where he developed his masters thesis on phylogenetic theory. In 2008, he started his PhD at the Institute of Evolutionary Biology (CSIC-UPF) and graduated from The Autonomous University of Barcelona. After his PhD, Talavera held positions at the Institute of Evolutionary Biology (CSIC-UPF) (Barcelona) (2017-2020), Harvard University (2014-2018), the Museum of Comparative Zoology (MCZ – Harvard Univesity (2015-2020) and at St. Petersburg State University (Russia) (2013-2014). During his career, he has been awarded with highly competitive fellowships.
Dr. Gerard Talavera. Credit: Dr. Gerard Talavea.
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Publish date : 2024-07-28 13:00:00
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